In recent years, compact sensor terminals having wireless functions (sensor node communication terminal) containing a power supply have been developed. Such sensor node communication terminals have been installed over a plurality of outdoor building structures (e.g. bridges, roads, railroad service, buildings, and the like), for example, and used for measurements and analyses of environmental information including various physical quantities, e.g. temperatures, humidity, amounts of strain, etc.
There are applicabilities to monitoring of health conditions of infrastructures by introducing such sensor node communication terminals to structures of social infrastructures so as to execute sampling the information. More specifically, there have been proposed variously wireless sensor network systems in which measured data transmitted from a plurality of sensor node communication terminals is received and stored in host communication terminals, and thereby states of building structures etc. are automatically measured in order to monitor the states thereof on the basis of the measured data.
Such above-mentioned building structures, such as bridges, roads, railroad services, buildings, etc., are gradually over-aged by aged change/deterioration due to winds and rains, vibrations, etc. with the lapse of years since the building structures constructed.
Accordingly, there have been spread so-called conceptions of Structural Health Monitoring (SHM) for monitoring progress and positions of deteriorations, etc. in these building structures using such sensor network systems, and predicting timing for performing maintenance (e.g. repairs), before breakage or destruction of the building structures.
It is said that lifetimes of infrastructure constructions which are sensor objects are several tens of year. On the other hand, ordinary electronic components composing sensor node communication terminals do not have sufficient working lifetimes.
For example, although working lifetimes of building structures, e.g. bridges, are supposed to be approximately tens of years, working lifetimes of sensor elements composed by including several kinds of electronic components are from approximately five years to approximately ten years (depending on kinds of the electronic components). Accordingly, in order to continuously perform the structural health monitoring over several tens of years with respect to the infrastructure constructions which are sensor objects, maintenances are required for exchanging the sensor elements or sensor node communication terminals itself in accordance with deterioration states or failed states, etc.
However, since conventional sensor node communication terminals include only one sensor element therein as a sensor configured to detect each physical quantity, the sensor element detected only states where operations of the sensor element are stopped due to expiration of lifetimes or occurrence of failures.
Moreover, when sensor data (measured data) continuously or intermittently transmitted from each sensor node communication terminal is received in host communication terminals, it was difficult to determine whether an abnormality is detected in structures which are sensor objects (i.e., whether the measured data is correct), or whether the measured data is incorrect (i.e., a failure occurs in the sensor node communication terminal), with regard to abnormal measured data.
Moreover, there was a problem that it is only understood that sensor elements mounted on sensor node communication terminals cannot execute sensing due to expiration of lifetimes or occurrence of failures.
Accordingly, there was a problem that it was difficult to predict timing of maintenance, such as replacement, before expiration of lifetimes or occurrence of failures of the sensor elements in conventional sensor elements, and thereby constituting an obstacle to continuous structural health monitoring.